JPH0611396B2 - Microcapsule manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an amine-aldehyde polycondensation used for the purpose of converting or controlling various properties in the fields of pharmaceuticals, agricultural chemicals, fragrances, dyes, pressure-sensitive copying paper, etc. More particularly, the present invention relates to a method for producing microcapsules having an amine-aldehyde polycondensation wall film effective for pressure-sensitive copying paper.

2. Description of the Related Art Various methods such as mechanical, physical, physicochemical, chemical methods, and combinations of these methods are known as methods for producing microcapsules.

The present invention belongs to a chemical method for forming a microcapsule wall film composed of an amine-aldehyde polycondensate by a reaction from only one of the continuous phases, that is, an in situ polymerization method. Further, the present invention does this in the presence of the specific copolymer anionic water-soluble polymer.

The method of using amine or urea and formaldehyde as the wall film forming material is described in, for example, JP-B-37-12380 and JP-B-44-379.
5, as described in Japanese Examined Patent Publication No. 47-23165. These methods have the drawbacks that the emulsification and dispersion are not carried out efficiently, or it is difficult to deposit the polycondensate around the hydrophobic core material efficiently and stably.

For the purpose of improving this point, JP-B-54-16949 proposes to use ethylene-maleic anhydride copolymer, acrylic acid polymer, methyl vinyl ether maleic anhydride copolymer, etc. as the anionic polyelectrolyte. ing. Although this method improved the emulsification and dispersion characteristics and the efficiency of depositing the polycondensate around the core substance, it still has drawbacks such as high viscosity of the finished capsule slurry.

Further, in JP-A-55-47139, a mixed use of a styrene maleic anhydride copolymer and a vinyl acetate maleic anhydride copolymer,
JP-A-56-51238 proposes the use of vinylbenzene sulfonic acid-based anionic polymer, and JP-A-56-58536 proposes the presence of a polymer or copolymer having a sulfonic acid group. . Further, JP-A-58-14942 discloses that in the presence of a copolymer anionic water-soluble polymer composed of acrylic acid, styrene sulfonic acid, and at least three monomers of hydroxyalkyl acrylate or hydroxyalkyl methacrylate. In JP-A-59-142836, a mixed use of an acrylic acid copolymer and a styrene-sulfonic acid type copolymer is used, and in JP-A-60-28819, acrylic acid, acrylonitrile and acrylamidoalkylsulfonic acid or a sulfoalkyl ester of acrylic acid is used. In JP-A-60-68045, a melamine-formaldehyde polycondensate or a urea-formaldehyde polycondensate is encapsulated in the presence of a copolymer of acrylic acid and an alkyl acrylate. A method of making a wall membrane is disclosed.

However, each of these techniques has the following problems to be improved. That is, in the case of JP-A-55-47139, the solubility stability of the sulfone-maleic anhydride copolymer at a pH of 4 or less is insufficient, and the vinylbenzenesulfonic acid-based anionic polymer of JP-A-56-51238 is used. When used for producing a capsule wall membrane of urea-formaldehyde polycondensate, it is difficult to obtain a dense capsule wall membrane, and a large amount of foaming occurs when the polymer is dissolved, resulting in poor workability during capsule production. JP-A-58-14942, JP-A-59-14283 and JP-A-60-68045 disclose that a slurry having a high concentration, a low viscosity and a good capsule particle size distribution can be obtained.
However, when these are used for pressure-sensitive copy paper, there is a drawback that spot-like stains are generated on the surface of the pressure-sensitive copy paper.
On the self-coloring type pressure-sensitive copying paper, the spot-like stains are noticeable. This cause is considered to be due to a large amount of huge particles and agglomerates present in the capsule slurry, and if a surfactant is used to remove these, a new problem is that the capsule wall becomes less dense and color develops. Dots occur. When the copolymer disclosed in JP-A-60-68045 is used, the emulsifying property and the emulsion stability are certainly improved, but the spot-like stain and the increase in viscosity of the copolymer itself over time are improved. There was room.

Problems to be Solved by the Invention As is apparent from the above description, the object of the present invention is to form a microcapsule wall film composed of an amine-aldehyde polycondensate by a reaction from only one of the continuous phases.
There is an improvement in the production method of microcapsules by in situ polymerization method. First, by reducing the huge amount of giant particles present in the capsule slurry, spot-like stains are reduced even when used for pressure-sensitive copying paper. Especially.

Furthermore, the emulsifying power is strong, the emulsion stability during the reaction is good, the particle size distribution of the finished capsule and the denseness of the capsule wall film are good, and the workability is also good. To do.

Means for Solving the Problems As a result of repeated studies to solve the above problems, the amine-aldehyde polycondensate was prepared in a system in which a hydrophobic core substance was dispersed or emulsified in an acidic aqueous solution containing an anionic colloid substance. A method for producing a microcapsule for forming a capsule as a wall film, wherein the anionic colloidal substance is a copolymer composed of acrylic acid, styrenesulfonic acid, and three kinds of monomers of alkyl acrylate or alkyl methacrylate. It has been found that the above problems can be solved by using an anionic water-soluble polymer.

As a method for obtaining the copolymer anionic water-soluble polymer of the present invention, a mixture of the above-mentioned three kinds of monomers is placed in a container to prepare an aqueous solution having an appropriate concentration, air in the container is replaced with nitrogen gas, and then polymerization is carried out. A radical polymerization method in an aqueous system, which is a general polymerization method of acrylic acid in which an organic or inorganic peroxide or persulfate is added as an initiator and a polymerization reaction is performed by heating, is preferable. After completion of the reaction, part of the copolymer may be neutralized with an alkali such as caustic soda, if necessary. A copolymer radical-polymerized in an aqueous system is generally obtained as an aqueous solution having a nonvolatile content of 5 to 30% by weight, and unlike a maleic acid-based copolymer, a dissolving operation is unnecessary and encapsulation work is simplified. .

The composition of the raw material monomer of the copolymer anionic water-soluble polymer of the present invention is preferably 73 to 92% by weight of acrylic acid, 2.5 to 17% by weight of styrenesulfonic acid, and alkyl acrylate or alkyl methacrylate having 6 or less carbon atoms. 2.5-22% by weight
And more preferably 80 to 90% by weight of acrylic acid, 3.5 to 10% by weight of styrene sulfonic acid, and 3.5 to 10% by weight of alkyl acrylate or alkyl methacrylate.

Further, as the alkyl acrylate, ethyl acrylate,
At least one selected from propyl acrylate and butyl acrylate is preferable, and as the alkyl methacrylate, at least one selected from ethyl methacrylate, propyl methacrylate, and butyl methacrylate is preferable.

The molecular weight of the copolymer anionic water-soluble polymer of the present invention is
50,000 to 500,00 in average molecular weight measured by gel permeation chromatography with exclusion limit molecular weight of 2,000,000 (PEG)
It is 0, preferably 100,000 to 300,000. The viscosity of the aqueous solution of the copolymer anionic water-soluble polymer of the present invention measured with a B-type rotational viscometer at a nonvolatile content of 25% by weight, pH 3.1, and 25 ° C. is 300 to
It is preferably 5,000 cps, more preferably 40 to 1,50
It's 0 cps. At 300 cps or less, the emulsifying power and emulsion stability are insufficient, so the particle size distribution tends to be broad and the number of giant particles tends to increase. On the other hand, when it is 5,000 cps or more, the viscosity during the reaction and the viscosity of the slurry become high, so that it is not suitable for low viscosity slurry such as pressure sensitive copying paper which is preferable.

The acrylic acid, styrene sulfonic acid, and the target copolymer anionic water-soluble polymer used in the present invention can be handled in the form of no salt or partial salt. The present invention also includes these salt forms. As the salt, lithium salt, sodium salt, potassium salt, magnesium salt and calcium salt are preferable.

The general method of practicing the invention is as follows.

(1) Preparation of core substance The hydrophobic liquid as the core substance of the capsule is used as it is, or another substance is dissolved in the hydrophobic liquid by heating and stirring if necessary to obtain the capsule core substance.

(2) Preparation of continuous phase The copolymer anionic water-soluble polymer of the present invention is diluted and dissolved in city water at room temperature to dissolve one of an amine or an aldehyde or an initial polycondensate thereof which forms a capsule wall film. As a continuous phase. These initial polycondensates may be modified with phenols or benzoguanamine.

The ratio of the wall membrane material to the core substance is 1: 1 to 1: 1 in terms of solid content weight ratio.
The amount of the copolymer anionic water-soluble polymer of the present invention used is 0.5 to 7% by weight of the capsule manufacturing system, and the type and wall of the copolymer anionic water-soluble polymer are used. Although it varies depending on the type of film-forming material, the type of core substance, the purpose of encapsulation, etc., 1 to 5% by weight of the capsule manufacturing system is a more suitable range. The amine and aldehyde, which are wall film forming materials, can be used alone or as a prepolymer in advance if they are dissolved in the continuous phase. The amine of the present invention includes urea, thiourea, melamine and their carbon number 1
~ 4 alkylated compounds, methylolated compounds and 1 to 4 carbon atoms
Or a mixture of alkylated methylol compounds of. Among these, it is preferable to use at least one of melamine, methylolmelamine, methylated methylolmelamine, urea, dimethylolurea, and methylated methylolurea.

Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, glyoxal, glutaraldehyde, methylglutaraldehyde, furfural and acrolein, of which formaldehyde is most preferable.

(3) Emulsification Next, the core substance solution is added to the above continuous coarse powder while stirring and emulsified by an emulsifying machine such as a homogenizer or a static mixer. Generally, it is preferable to carry out the emulsification at room temperature or lower temperature in terms of particle size distribution.

(4) Capsule Wall Forming Reaction When emulsion particles having a predetermined particle size are obtained, the pH of the aqueous solution is adjusted to a range in which the wall film forming material is polycondensed. Generally, when this reaction is carried out under acidic conditions, the wall film becomes denser. PH
The lower the pH, the faster the reaction, but considering that too rapid a reaction may hinder the formation of a uniform capsule wall, PH
Adjust up to about 3.

The ratio of amine and aldehyde cannot be determined unconditionally,
Usually, 0.6 to 0.5 mol of aldehyde is used for 1 mol of amine. As an example, in the case of urea and formaldehyde, 1.2 mol of formaldehyde is added to 1 mol of urea.
The preferred range is 3.0 mol.

The heating is started at the same time when the emulsification is completed or when the aldehyde is added. The temperature is heated to 35-90 ℃, but usually 50-75 ℃
Adjust to. After reaching the set temperature, it is preferable to keep the temperature for a certain time or longer, and in the case of the reaction at 50 to 60 ° C, it is preferable to keep the temperature for at least 1 hour.

(5) Post-treatment After encapsulation, adjust the temperature according to the purpose,
The pH is adjusted, washed, filtered, dried, and powdered. When formaldehyde is used as the aldehyde, the excess formaldehyde present in the slurry is usually reduced.

Action The details of the action of each monomer of the copolymer anionic water-soluble polymer of the present invention are not clear, but by analogy with the state when encapsulation is performed using each homopolymer, it is roughly the following. Is thought to be. Acrylic acid has an emulsifying dispersive power and accelerates the capsule wall forming reaction, but it is less effective in reducing giant particles, and tends to give a capsule slurry of relatively high viscosity.

Styrene sulfonic acid accelerates the emulsification rate, promotes capsule wall formation, and is effective in reducing macroparticles, but tends to give a relatively stiff and non-dense capsule wall membrane.

Alkyl acrylate or alkyl methacrylate does not accelerate the capsule wall forming reaction, improves the emulsifying and dispersing power, is effective in reducing the huge particles, and gives a low viscosity capsule slurry.

When hydroxyalkyl acrylate or hydroxyalkyl methacrylate is used instead of alkyl acrylate or alkyl methacrylate, the capsule wall formation reaction is promoted, but the emulsifying and dispersing power is slightly inferior, and the effect on the reduction of giant particles is insufficient. However, the properties of both are symmetrical. Both give low-viscosity capsule slurries, but the characteristic feature of the alkyl acrylate or alkyl methacrylate of the present invention is that it has a slightly lower viscosity, and that the viscosity rises less with an increase in PH.

Furthermore, when the number of carbon atoms in the alkyl group is 7 or more, the viscosity during the reaction for forming the capsule wall is severe and the formation of the capsule wall film may be insufficient or impossible.

The copolymer anionic water-soluble polymer of the present invention exhibits the action as described above by copolymerizing acrylic acid, styrenesulfonic acid and alkyl acrylate or alkyl methacrylate having 6 or less carbon atoms. It is thought that it will appear for the first time.

EXAMPLES Hereinafter, the present invention will be described by taking a microcapsule for pressure-sensitive copying paper as an example, but this is merely for convenience of description, and the present invention is not limited to the pressure-sensitive copying paper or the examples.

Parts and% in the examples represent parts by weight and% by weight.

The capsule slurries obtained in the following Examples and Comparative Examples were measured and tested in the following manner with the viscosity of the slurry, the emulsifying power (average particle size), the particle size distribution and the number of giant particles as evaluation items, and the results. Is shown in Table 1.

Viscosity: The viscosity of the capsule slurry at 25 ° C was measured with a B-type rotational viscometer.

Emulsifying power: The emulsifying power was evaluated by the average volume particle size of the emulsified particles when emulsified under the same conditions. Coulter counter TA
-II type particle size analyzer (made by Coulter Electronics)
I went to.

Particle size distribution: The particle size distribution was expressed by 10 times the logarithm of the particle size ratio of the particle size at 25% volume point and the particle size at 50% volume point by Coulter Counter TA-II type particle sizer. Regardless of the average particle size, the smaller this value, the narrower the particle size distribution.

Giant particles: The number of huge particles is so small that it cannot be measured by a commercially available particle sizer. The capsule slurry produced there was diluted twice with city water and applied to the lower paper for pressure-sensitive copying paper (W-50BR manufactured by Tojo Paper Co., Ltd.) with a wire bar No. 22,
dry. The number of spot-like color stains appearing on the lower paper is expressed by the number in an area of 10 × 20 cm. It is considered that this spot-like contamination is due to giant particles or secondary agglomeration existing for some reason.

[Example 1] Acrylic acid 80 parts, styrene sulfonic acid partial sodium salt
Nonvolatile content 25%, consisting of 10 parts, ethyl acrylate 10 parts,
A copolymer anionic water-soluble polymer having a viscosity of 1,150 cps (B-type viscometer at 25 ° C) was synthesized. Dissolve 28 parts of this product with 72 parts of water, further dissolve 10 parts of urea and 1.2 parts of resorcin,
The pH of this mixed solution was adjusted to 3.4 with an aqueous sodium hydroxide solution. Separately, to 148 parts of a high-boiling solvent containing phenylxylylethane as a main component, 6 parts of crystal bio lettlactone as a colorless dye is added and dissolved at 90 ° C. with stirring. After dissolution, the mixture was cooled to room temperature and mixed in an aqueous solution containing the previously prepared copolymer anionic water-soluble polymer while paying attention to phase inversion, and then using a homomixer (manufactured by Tokushu Kika Co., Ltd.),
The emulsion was emulsified at 9,000 rpm for 10 minutes to obtain a stable O / W emulsion having an average particle diameter of 3.5μ. Then, 27.5 parts of diluting water and 23.5 parts of 37% formaldehyde were added and heating was started. After reaching 55 ° C, the capsule wall forming reaction was continued for 2 hours. A small amount of the completed capsule liquid was put into a 20% resorcin solution and shaken to see the completion of the capsule wall. No change was observed (immediately turns blue when the completion of the capsule wall is insufficient).
A dense wall film was formed.

In order to reduce residual formaldehyde, 28% ammonia water was added to PH7.5 after cooling to 40 ° C. to obtain a capsule slurry of pressure-sensitive copying paper.

[Examples 2 to 5] The same monomers as in Example 1, that is, four kinds of copolymer anionic water-soluble polymers prepared by changing the composition ratio of acrylic acid, styrenesulfonic acid partial sodium salt, and ethyl acrylate were used. Then, a capsule slurry was manufactured by the same procedure as in Example 1.

[Examples 6 to 15] A copolymer anionic water-soluble polymer in which the composition ratio of acrylic acid, styrenesulfonic acid and propyl acrylate or n-butyl acrylate was changed in the same manner as in Example 1 was synthesized. Using this, a capsule slurry was produced in the same procedure as in Example 1.

[Examples 16 to 18] Three types of copolymer anionic water-soluble polymers obtained by polymerizing 80 parts of acrylic acid, 10 parts of styrenesulfonic acid and 10 parts of ethyl methacrylate, 10 parts of propyl methacrylate, and 10 parts of n-butyl methacrylate. Capsule slurry was manufactured in the same procedure as in Example 1 using the polymerizable polymer.

As is clear from Table 1, the evaluation results of the capsules obtained in Examples 1 to 18 indicate that not only the number of giant particles seen as spot contamination is almost absent but also the emulsifying power, particle size distribution, and viscosity of the slurry should be satisfied. As shown in Example 1, the capsule wall film was excellent in denseness as well.

80 parts of acrylic acid obtained in Example 16, 10 styrene sulfonic acid
Copolymer of the present invention consisting of 10 parts of ethyl methacrylate and 10 parts of ethyl methacrylate, and a copolymer of 80 parts of acrylic acid and 10 parts of styrene sulfonic acid and 10 parts of hydroxyethyl methacrylate of Comparative Example 7 described below. When the time-dependent change in the viscosity of the combined anionic water-soluble polymer was examined, it was as follows.

Example 16 Comparative Example 7 Immediately after production 770 cps 1,050 cds After 3 weeks 800 2,500 After 2 months 850 6,300 After 6 months 840 25,300 Thus, the copolymer anionic water-soluble polymer of the present invention contains a hydroxy group. Compared with the copolymer disclosed in Sho 60-68045, it is a stable polymer with very little change in viscosity over time, and is useful in the production of microcapsules.

Example 19 Nonvolatile content 25% consisting of 85 parts of acrylic acid, 7.5 parts of styrene sulfonic acid and 7.5 parts of n-butyl acrylate, viscosity 900 cps
(25 ° C B-type viscometer) A copolymer anionic water-soluble polymer was synthesized, 28 parts of this was added to 100 parts of city water, diluted and dissolved, and then PH was adjusted to 4.0 with a 20% caustic soda aqueous solution. To this was added 154 parts of the same colorless liquid hydrophobic liquid solution as in Example 1,
The emulsion was emulsified in the same manner as in Example 1 to obtain a stable emulsion of O / W type having an average particle size of 4.0 μ. While stirring, 26 parts of a methylated methylolmelamine initial condensate aqueous solution (nonvolatile matter 80%, Euramine P6300, manufactured by Mitsui Toatsu Kagaku Co., Ltd.) was added, and a capsule film forming reaction was carried out at 55% for 2 hours. A small amount of the completed capsule slurry was put into a 20% aqueous resorcin solution, shaken, and when the completion of the capsule wall was observed, no change was observed and a dense capsule film was formed. Further, in order to reduce residual formaldehyde, 28% ammonia aqueous solution was added until pH 7.5 after cooling to 40 ° C. to obtain a capsule slurry for pressure-sensitive copying paper.

Even when the wall membrane material is a methylated methylol melamine resin as well as the urea formaldehyde resin, there are few large particles due to the use of the copolymer anionic water-soluble polymer of the present invention,
It can be seen from Table 1 that a low-viscosity capsule slurry having a good particle size distribution and a good dense wall film is obtained.

Comparative Example 1 A copolymer of 90 parts of acrylic acid and 10 parts of ethyl acrylate and having a nonvolatile content of 25% and a viscosity of 1020 cps (B-type viscometer at 25 ° C.) was used. Similarly encapsulated.

[Comparative Examples 2 to 6] 90 parts of acrylic acid, propyl acrylate, and n-acrylic acid
Butyl, ethyl methacrylate, propyl methacrylate,
A capsule slurry was prepared in the same manner as in Example 1 using 5 kinds of copolymer anionic water-soluble polymers obtained by copolymerizing 10 parts of methacrylic acid and n-butyl methacrylate.

Comparing the evaluation of the capsules with those of Examples 1 to 5, the capsules of Comparative Examples 1 to 6 containing no styrene sulfonic acid had more than five times the number of giant particles observed due to spot contamination, and the completed capsule slurry. Although the viscosities were the same, the viscosity increased sharply during the capsule wall forming reaction, which was not preferable in the capsule manufacturing operation. Furthermore, the emulsifying power is weak,
The particle size distribution was also somewhat poor.

[Comparative Examples 7 to 9] A non-volatile content of 25% consisting of 80 parts of acrylic acid, 10 parts of styrenesulfonic acid and 10 parts of hydroxyethyl methacrylate, hydroxy n-butyl methacrylate or hydroxyisobutyl methacrylate, and a viscosity of 1,050 cps, 865cps,
Encapsulation was performed in the same manner as in Example 1 using three types of copolymer anionic water-soluble polymer at 750 cps (25 ° C. B-type viscometer).

This comparative example is an example of encapsulation by a copolymer using hydroxyalkyl methacrylate instead of alkyl methacrylate of the copolymer anionic water-soluble polymer of the present invention. Comparing the evaluation results with those of Examples 16 to 18 in Table 1, the emulsifying power, the particle size distribution and the viscosity of the capsule slurry are almost the same, but the number of giant particles is large and this is inferior. is there. Further, as described in Examples 16 to 18, the copolymer anionic water-soluble polymer using hydroxyalkyl methacrylate has a drawback that its viscosity with time increases remarkably, which is not preferable in capsule manufacturing work.

[Comparative Examples 10 to 11] 90 parts of acrylic acid, 5 parts of styrene sulfonic acid and 5 parts of octyl acrylate, and a viscosity of 1,25 at a nonvolatile content of 25%.
Copolymer anionic water-soluble polymer at 0 cps (25 ° C B type viscometer) and viscosity 970 cps at 25% non-volatile content consisting of 85 parts of acrylic acid, 10 parts of styrene sulfonic acid and 5 parts of lauryl methacrylate. Type viscometer) and two types of copolymer anionic water-soluble polymer were used for encapsulation in the same manner as in Example 1.

The emulsification was good and the emulsifying power was strong, the particle size distribution of the emulsified particles was good, and although there was a slight increase in viscosity during the capsule wall formation reaction, it did not gel, but the finished capsule slurry was 20%. Immediately after a small amount was put into the resorcin solution, it turned blue, and the capsule slurry was allowed to flow gently on the lower paper for pressure-sensitive copying paper and allowed to dry naturally, and the entire surface of the lower paper turned blue. Therefore, no substantial capsule wall film was formed on the hydrophobic core substance in these capsule slurries.

Effects of the Invention The copolymer anionic water-soluble polymer of the present invention is
Microcapsules with significantly less giant particles than conventional methods can be obtained by using microcapsules made of aldehyde polycondensates for the production of microcapsules by the in situ polymerization method, which is formed by the reaction from only one of the continuous phases. A slurry is obtained. Furthermore, the emulsifying power is strong, the particle size distribution of the obtained emulsified particles is good, and the viscosity of the resulting capsule slurry is low, so it is easy to handle despite a high-concentration capsule slurry, and a high-concentration paint can be obtained. It can be efficiently applied to a support such as paper.

Further, since the copolymer anionic water-soluble polymer of the present invention does not contain a hydroxyl group, the viscosity does not increase with the passage of time, and is also excellent in this respect.

Claims (5)

[Claims] 1. A method for producing microcapsules, which comprises forming a capsule having an amine-aldehyde polycondensate as a wall film in a system in which a hydrophobic core substance is dispersed or emulsified in an acidic aqueous solution containing an anionic colloid substance. The above-mentioned anionic colloidal substance is a copolymer anionic water-soluble polymer composed of acrylic acid, styrenesulfonic acid, and three kinds of monomers of alkyl acrylate or alkyl methacrylate having an alkyl group having 6 or less carbon atoms. A method for producing a microcapsule characterized by being present. 2. The copolymer anionic water-soluble polymer is 75 to 90.
% Of acrylic acid, 2.5 to 20% by weight of styrene sulfonic acid, 2.5 to 20% by weight of alkyl acrylate or alkyl methacrylate having an alkyl group having 6 or less carbon atoms. The method for producing the microcapsule according to item 1. 3. In the alkyl acrylate or alkyl methacrylate constituting the copolymer anionic water-soluble polymer, the alkyl acrylate is selected from at least one of ethyl acrylate, propyl acrylate or butyl acrylate, and methacrylic acid is used. The method for producing microcapsules according to claim 1 or 2, wherein the alkyl acrylate is selected from at least one of ethyl methacrylate, propyl methacrylate, and butyl methacrylate. 4. The amine-aldehyde polycondensate constituting the capsule wall membrane is an amine and formaldehyde selected from at least one of melamine, methylolmelamine, methylated methylolmelamine, urea, dimethylolurea, and methylated dimethylolurea. Or a prepolymer thereof, Claim 1.
Item 4. A method for producing a microcapsule according to any one of items 3 to 3. 5. The method for producing microcapsules according to claim 4, wherein the capsule wall film is a urea-formaldehyde polycondensate.